A copper ball 2 cm in radius is heated in a furnace to 327 °C. If its emissivity is 0.3, at what rate does it radiate energy?

• 1.72 W

• 2.73 W

• 11.0 W

• 2.15 W

• higher than 0°C

• higher than 0 K

• higher than that of its surroundings

• high enough for it to glow

Young's modulus for a steel wire is 2 x 10¹¹ Pa and its elastic limit is 2.5 x 10⁸ Pa. By how much can a steel wire 3 m long and 2 mm in diameter be stretched before the elastic limit is exceeded?

• 3.75  mm

• 7.50 mm

• 4.75 mm

• 4.00 mm

Assertion:  In an isolated system the entropy increases. 

Reason:  The process in an isolated system is adiabatic only.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion:  The fundamental frequency of an open organ pipe increases as the temperature is increased. 

Reason:  This is because as the temperature increases, the velocity of sound increases more rapidly than length of the pipe.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion:  A hollow metallic closed container with small opening maintained at a high temperature can act as a source of black body radiation.

Reason:  All metals act as black body radiator.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

The force per unit length between two straight conductors separated by a distance of 0.02 m is 2 x 10^-3 N m^-1. The current in one conductor is 10 A and that in the other conductor is

• 20 A

• 5 A

• 2 A

• 10 A

What is the equivalent resistance between A and B in given figure?

• 50 Ω

• 25 Ω

• 75 Ω

• 100 Ω

What is the magnetic field on the axis of a coil of radius r carrying current I at a distance R from the origin?

• $\frac{{\mathrm{\mu }}_0 \mathrm{I} {\mathrm{r}}^2}{2 {\left({\mathrm{r}}^2 + {\mathrm{R}}^2\right)}^{{\displaystyle \raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}}}$

• $\frac{{\mathrm{\mu }}_0 {\mathrm{IR}}^2}{2 {\left({\mathrm{r}}^2 + {\mathrm{R}}^2\right)}^{{\displaystyle \raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}}}$

• $\frac{{\mathrm{\mu }}_0\mathrm{I}}{2 \left(\mathrm{r} + \mathrm{R}\right)}$

• $\frac{{\mathrm{\mu }}_0 \mathrm{IR}}{2 {\left({\mathrm{r}}^2 + {\mathrm{R}}^2\right)}^{{\displaystyle \raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}}}$

30.

The temperature of transition from ferromagnetic property to paramagnetic property is called

• Transition temperature

• Critical temperature

• Curie temperature

• Triplet temperature